The fate of hepatitis B vaccine candidate Heplisav-B has sent developer Dynavax’s shares, and its investors, on a wild ride in recent days. A request by the FDA for more details of the vaccine’s postmarketing surveillance plan sent the company's stock slightly downward, but both management and analysts said they remain confident in approval.

Given the closeness of the FDA's action date for the vaccine on August 10, Dynavax said that after discussion with the agency they have agreed to extend the review date for up to three months to finalize details of the postmarketing study.

The agency’s request mainly centers on ensuring accurate, timely collection of real-world safety data from Heplisav-B use.

During an analyst call Thursday afternoon, Dynavax CEO Eddie Gray stressed that the FDA’s request is “wholly consistent with” what the agency's expert panel had expressed earlier in the week. During that panel, experts voted 12 to 1 in favor of the shot’s safety profile, a result that sent Dynavax’s stock to a one-year high. But the panel also raised concerns about the proposed design of the surveillance program.

“This delay … does not in any way impact our confidence that the vaccine should be approved or our internal launch plans and timeline,” Gray said during the call.

Perhaps because the issue was already well expressed during the FDA panel discussion, Dynavax's share price is gradually recovering from a slight slip Friday. At least one analyst shared Dynavax’s optimism.

“We don’t view this delay as fundamentally changing the narrative, and continue to see approval as a matter of when, not if,” RBC Capital Markets analyst Matthew Eckler wrote in a note to investors. “The recent positive FDA AdCom was a key derisking event for Heplisav-B, and given the vaccine’s superior profile, it has the potential to capture significant market share, as well as drive expansion.”

Eckler previously projected that the vaccine could reach peak U.S. sales of $290 million in 2026.

Under the current plan, Dynavax is aiming to launch the shot, a challenger to GlaxoSmithKline’s Engerix-B, in the U.S. in early 2018. It's proposing to conduct the phase 4 study in collaboration with Kaiser Permanente Northern California to monitor medical records for 20,000 Heplisav-B recipients against 20,000 others who receive the GSK shot during a 12-month follow-up. It's likely that cardiac incidents, for which an imbalance was seen in a phase 3 study, will be the main focus.

Gray added that the company is on track to present to the CDC’s Advisory Committee on Immunization Practices at their meeting in late October, even if it’s before the Nov. 10 FDA decision deadline.